Joint for fluid filled cables and method of making the same



1, 1936. L PH|LL|PS 2,053,163

JOINT FOR FLUID FILLED CABLES AND METHOD OF MAKING THE SAME Filed Aug. 18, 1930 30 l9 l5 pigl.

, Inventor: Lesber L. Phil li'ps,

466 His Abborneg.

Patented Sept. 1, 1936 PATENT OFFICE JOINT FOR FLUID FILLED CABLES AND METHOD OF MAKING THE SALE Lester L. Phillips, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application August 18,

4 Claims.

The present invention relates to electric cable having a channel located within the enclosing sheath which is maintained continuously filled with a suitable insulating fluid, such as thin oil,

and from which cable and fluid gases and moisture are carefully excluded at all times. Cables of this character when shipped from the manufacture to the customer are usually filled with fluid and carefully sealed, and are also provided with means for compensating for changes of volume of the fluid due to changes of temperature.

Under the conditions specified the problem is presented of joining reel lengths of cable into a complete cable system without appreciable loss of fluid on the one end, or the admission of gases and moisture on the other. The same problem is presented in connecting the ends of the cable to the terminals.

The object of my invention is the provision of improved and simple means for joining reel lengths of cable having fluid channels, and for joining the ends of such cable to its terminals in such manner that appreciable loss of insulating fluid will be prevented and at the same time the admission of gas and moisture to the cable is also prevented.

For a consideration of what I believe to be novel and my invention attention is directed to the accompanying description and the claims appended thereto.-

In the drawing which is illustrative of my invention, Fig. 1 is a view of a cable joint in quarter section; Fig. 2 is a detail view of one type of cable having an exterior channel; Fig. 3 is an enlarged view of a semifiuid stop joint; Fig. 4 is a view illustrating two reel lengths of cable which have been installed, for example, in a conduit, and Fig. 5 is a sectional view of a modified form of thimble.

Referring first to Fig. 2, 5 indicates a conductor made of numerous small wires, 6 the pervious insulation thereon such as paper, 1 a metal band which is wrapped around the paper between it and the sheath 8. Over the insulation is wrapped a thin metal ribbon ll forming an electrostatic shield which is in electrical contact with the band 1. The shield has numerous perforations 42 to permit oil from the channel to freely penetrate the paper insulation. Formed integral with the band 1 and on the side edges thereof are well rounded projections 9 which engage the inner wall of the sheath, said projections being open at the side to prevent trapping of gases. By this arrangement an annular channel I0 is provided between the insulation and 1930, Serial No. 476,228

band on the one hand and the inner wall of the sheath 0n the other. This channel is filled with insulating fluid which for convenience will be termed oil, and said oil is maintained under a pressure which is slightly above that of the atmosphere during the period of shipping and installing and may be considerably higher when in operation. The oil, due to its characteristics, freely permeates the paper insulation about the conductor. It is to prevent oil from escaping 10 from this annular channel during installation that my invention is especially directed.

Referring now to Fig. 1, II and I2 indicate two cable lengths or sections which are to be joined, each length being of the character described in 15 connection with Fig. 2. I3 indicates the connector which is soldered or otherwise secured to the conductor ends. i4 indicates the permeable paper insulation in the form of ribbon which is Wound around the conductors to the desired thickness. On opposite sides of the joint the paper insulation is reduced by steps l5. On these steps is wound oil saturated candle wicking l6. Over the connector and stepped ends of the insulation is wound suitable tape insulation IT. For this purpose varnished cloth or cambric may be used which has high insulating properties and is impervious to oil. Outside of this a second body of tape 18 is wound which may be of the same kind as the first. Between all of the layers of tape a 30 suitable insulating compound is applied with a brush. The second body of tape has its ends tapered and over it is an electrostatic shield I9 which for example may be in the form of fine wire netting or metal braid. In some cases the shielding may be omitted from the central part of the body I8 and only its tapered ends covered. In any event the small ends of the shield must be electrically connected to the lead sheaths. Surrounding the joint and sealed at its ends to the cable sheaths as by wiped soldered joints, is a casing 20, which may be made of brass, lead or other suitable material. I

The means for preventing the escape of 011 from the channel during the jointing operation will iow be described, and more especially in connection with Fig. 3 which is on a larger scale. 25 indicates a thimble made of copper or other suitable metal the wall of which is thin. It has two diameters, the larger part making a close fit with a wall of the sheath, in this case the inner, and the smaller part making a close fit With the covering on the cable, in this case the ribbon or electrostatic shield M. Because of the telescopic relation of the thimble and associated parts it can easily be adjusted to its proper position. Generally speaking, it is better to slip the enlarged end of the thimble inside of the sheath rather than over it because by so doing the diameter can be less and a better mechanical joint made because the lead sheath can be hammered down to make a snug fit around the thimble. The thimble being cylindrical is well adapted to withstand blows without crushing. The thimble is also provided with a radial boss 26 containing a port, the wall of which is screwthreaded to receive a socketed pipe plug 21 that acts as a valve or means for controlling the flow of. oil through the port as will appear later. It will be seen that the thimble and the covering on the conductor between them define a chamber M which is in free communication with the channel Ill. Surrounding the thimble and adjacent ends of the sheath and conductor covering is a body of varnished cambric tape 28. This material is chosen because it is impervious to the oil used in the installation. Soldered or otherwise connected to the shielding ribbon M is a band 33 which is also soldered to the shield is. This band is electrically connected or grounded to the lead sheath 8 by a strip of metal 29 which may extend axially or be wrapped around the insulation on the thimble. Its ends are soldered to the band 63 and to the sheath. When the thimble is fully taped only the outer ends of the boss and plug 27 are exposed. When the cable is in service one or both of the plugs 27 may be removed as desired to open a port or ports through one or both of the bosses. When only one is removed the oil from its section of the cable will be depended upon to maintain the supply of oil in the joint casing. That is to say, oil is free to pass from the annular channel within the sheath into and through the thimble and open port into the chamber 30 defined by the joint casing and the peripheral surfaces of the joint parts. In this manner the formation of voids within the casing is prevented.

The casing 20 is provided with two or more bosses 3i which are screw-threaded to receive either pipes or pipe plugs 32. The opening in each boss also forms a port and the plug a valve for controlling the flow of oil through it.

As a part of the jointing operation it is necessary to evacuate the chamber 30 within the casing to remove gases and to fill the same with de- For this purpose a vacuum pump 33 and a sealed tank 34 containing oil under pressure are employed. The tank may be elevated so as to give the desired oil pressure or it may contain elastic walled cells 35. A simple arrangement is to provide a T-shaped pipe and connect one branch to the pump, a second to the oil tank and the third to the casing either through the opening in one of the bosses 36 or that in a third boss 32a, as shown. In the T-shaped pipe are valves 36 and 37 to control the actions of the tank and pump respectively. When the cable is in service an oil reservoir generally resembling the tank will be connected to some or all of the joint casings. In any event, provision is made at suitable points along the length of the cable to take care of expansion and contraction of the oil.

As has been previously stated, each thimble is provided with a boss containing a port and a screw-threaded plug. When the parts are assembled the two plugs carried by the two thimbles should be in alignment with the bosses on the casing so that a wrench maybe inserted through wise.

one of the outer openings from which its plug is temporarily removed whereby the plug or valve 21 may be unscrewed and removed to establish communication for the oil from the channel at in the cable to the chamber 38 in the casing.

In Fig. 4 is shown a part of two lengths of cable which are to be united. Ordinarily these cable lengths will be contained in underground conduits although they may be above the surface of the earth. Each cable length has an end cap 38 which may be the pulling head for the reel length or a special cap. To the cable at a point remote from the place where the joint is to be made is provided a reservoir 39 containing degasified oil under pressure which is connected to the channel Ill in such manner as to feed oil thereto. The reservoir may contain a number of sealed cells having flexible walls for imparting pressure to the oil, or the reservoir may be elevated to create the necessary pressure. In the pipe leading from the reservoir is a control valve M.

In Fig. 5 is shown a modified form of construction of the thimble which is useful in those cases where for any reason there is a tendency for the parts inside the thimble to swell and thus enlarge the diameter. Any such swelling would tend to restrict the flow of oil through the port in the boss 26. To obviate this the thimble instead of having a single wall has a double wall, the parts of which are concentric. This may be made of two tubes 44 and 45, tube 65 being reduced in diameter at one end, as by a spinning operation, to snugly fit the corresponding end of inner tube 46 after which the joint between the tubes is completed at 46 by soldering or other- In this case the inner tube will fit or telescope over the covering on the conductor for a considerable distance and thus prevent any tendency of the covering to swell or enlarge and a free passage for oil from the channel It] to the ported boss will be maintained. Between the inner and outer tubes there is an annular chamber 31 which is in free communication with the channel in the adjacent cable. The passage of fluid to and from this chamber is controlled by the valve plug 2?.

The procedure in installing a joint, considering one length at a time, is as follows: The end of a cable length to be jointed is inclined upwardly as shown in Fig. 4 and the end cap removed, as by sawing ofi the end of the cable. Due to its upwardly inclined position, air will be prevented from working into the cable, and at the same time the valve is opened sufliciently to let a small amount of oil flow from the exposed or open end to further prevent the admission of foreign matter. The casing 2c is slipped endwise over one of the cable ends, or if made in two parts, one half is slipped over a cable end. The lead sheath is cut back and removed for the proper distance, and also the exposed part of the channel forming band I. The thimble 25 is then mounted in place by an endwise movement which also pushes one or more turns of the band back out of the way. If the end of the sheath has been expanded it is hammered down over the large end of the thimble to make a good mechanical joint. The next step is to wind the tape 28 which,

wound around it, or I may use a strap or connector to connect the shield I9 to the sheath 8. This being done, the plug 21 is removed and the valve opened to permit oil from the reservoir 39 and cable to flush out foreign matter, after which the plug is reinserted. The end of the cable is then prepared for jointing by removing insulation in the manner indicated on the drawing. The opposite cable end is similarly treated after which the ends are bent down to place with the ends of the conductors located within the connector. After the connector is soldered or otherwise united to the conductors the whole joint is insulated and shielded, as shown, and the casing moved endwise to place and connected to the cable sheaths by wiped soldered joints. Having properly assembled the casing in place, it is evacuated by the vacuum pump 33, the valve 31 being open for the purpose and valve 36 closed. When a satisfactory degree of vacuum is established valve 31 is closed and valve 36 opened which permits oil to flow into the casing and completely fill the same. The next step is to remove the aligned plugs or valves 32 and 21, oil from the tank 34 in the meanwhile flowing slowly outward to prevent admission of foreign matter. After plug 32 is removed a wrench is then inserted through the port or opening in the boss 3| into the socket in the plug 21 and the latter removed. after which the port in the boss 3| is closed. Under these conditions oil from the channel III of one cable section or length will supply oil through the opening in the thimble or receive it from the chamber 30 of the casing. If desired, one or both plugs 21 may be removed in the same manner depending upon how it is desired to supply the joint. If both are open oil can freely flow from one cable length to the other. The reservoirs may be connected to the parts of the casing in any suitable manner. In all cases when an opening is temporarily made in the casing oil should be permitted to flow outwardly through the port so long as it is opened to prevent entrance of foreign matter.

Owing to the fact that oil can very slowly mi grate or seep from the channel I0 into and through the paper insulation 14 and thence into the corresponding parts of the connected cable section, my improved joint may be termed a semistop joint as distinguished from a positive stop joint where all flow ormigration is prevented,

but for the purpose intended, it afiords a simpleyet adequate means for preventing the loss of oil from a cable end during splicing which would otherwise be great and which might result in requiring the whole cable length to be retreated in the field, which is a very expensive operation. Moreover the arrangement, due in part to the external control of the plug or valve 27, permits of shutting off the flow of oil to a casing whereever it is desired to open the same for inspection or other purposes.

The same construction of thimble may be used when connecting a cable length to an end terminal. In this connection the casing of a joint may be considered as illustrating the casing of the terminal.

Further advantages of my improved construction reside in the fact that no special tools of any sort are required, that the joints may be installed by a jointer of ordinary skill and on account of the character of the thimble special accuracy in cutting or positioning of the parts is unnecessary.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric cable having insulated conductors, a connector uniting the conductors, enclosing sheaths, a covering of insulation for each of the conductors, a fluid containing channel located between the insulation and one of the sheaths, a tubular means one end of which engages the wall of a sheath and the other end the covering on a conductor and defines a fluid containing chamber, a radially extending boss on the tubular means having a port through which fluid may flow from the chamber when it is open,

a plug for closing the port, a wrapping of insulation which covers the tubular means, except for the port, and seals it at one end to the sheath and at the other end to the covering on a conductor, a wrapping of insulation which covers the connector and that portion of the cable adjacent the tubular means, an electrostatic shield surrounding the last mentioned wrapping, a connector which overlies the insulation on the tubular means and is electrically connected at one end to the sheath and at the other end to the shield, and a fluid tight casing which encloses the aforesaid parts and is joined to the sheath at one end.

2. A pair of electric cables having fluid containing channels under their sheaths, in combination with a connector for uniting the cable ends, insulation therefor, a pair of spaced metallic thimbles, each of which engages a sheath at I one endand the covering on a cable section at the other end to define a fluid-containing chamber and has a controllable outlet port, insulation which covers the thimbles, and an electrostatic shield which overlies the insulation on the connector and that on the thimbles and is electrically connected at its ends. to said sheaths.

3. A cable joint comprising insulated conductors, a metallic sheath for each conductor, electrostatic shields covering the insulation on both'conductors, means between the shields and sheaths for defining a fluid channel, a connector electrically uniting the conductor ends, a. body of insulation for the connector and adjacent ends of the conductors, an electrostatic shield for .said body, thimbles each of which engages a sheath at one end and the electrostatic shield on a conductor at the other to define a chamber, a port in each thimble through which fluid may flow, insulation which surrounds each thimble and the adjacent parts, and means electrically connecting the electrostatic shield around said gaging the sheath and the inner wall of the thimble engaging the covering on the conductor.

LESTER L. PHILLIPS. 

